Evaporative pre-cooler for air cooled heat exchangers

ABSTRACT

The pre-cooler includes one or more cells which are oriented about an air stream to be cooled. A housing defines a perimeter of the cell with an inlet and outlet for air passing therethrough. Water outlet nozzles within the housing are preferably supported upon bars which orient the nozzles facing in a direction counter to flow of air through the housing. Each nozzle is coupled to a separate stage with multiple stages of nozzles coupled to separate valves. A controller opens or closes different valves. The controller measures ambient humidity and temperature conditions as well as air flow rates to calculate the amount of water to be added to the air and then opens appropriate numbers of stages of valves so that an appropriate number of nozzles spray water into the air to saturate the air. Flow rate control is thus provided without pressure variations, for optimal nozzle performance.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit under Title 35, United States Code§119(e) of U.S. Provisional Application No. 61/273,008 filed on Jul. 29,2009.

FIELD OF THE INVENTION

The following invention relates to evaporative coolers which add waterto unsaturated air to cause a temperature of the air to be reduced. Moreparticularly, this invention relates to evaporative pre-coolers for useupstream of an inlet air stream of a heat exchanger or other airreceiving mechanical equipment, such as a gas turbine, to improve thethermodynamic performance and/or heat transfer effectiveness of theequipment.

BACKGROUND OF THE INVENTION

The efficiency of both air cooled heat exchangers and gas combustionturbines, as well as other mechanical equipment increases as airtemperature decreases. Furthermore, such equipment also generallyincreases in efficiency as the mass of the air increases, such as highor humidity air versus lower humidity air. Water (and other liquids)when provided in liquid form adjacent unsaturated air will tend toevaporate into the air. This evaporation will continue until the air issaturated. Air is saturated with water in different amounts based on thetemperature of the air, with hotter air taking a larger amount of waterbefore reaching saturation.

A known phenomena when water evaporates into unsaturated air is that theair is cooled. The water transitioning from a liquid state to a gaseousstate is transitioning from a lower energy state to a higher energystate. The energy required for this transition to take place is providedto the water in the form of heat that is taken out of the surroundingair. This latent heat of vaporization leaving the air causes atemperature of the air to be reduced.

A device which utilizes this principle for cooling is often referred toas an evaporative cooler. Another term for such a device, when used forair conditioning of a residential space, is a “swamp cooler.” Suchevaporative coolers come in a variety of different configurations. Inone configuration, evaporative pre-coolers are placed upstream of heatexchangers such as those provided in a direct expansion air conditioningsystem, an air cooled chiller, a process cooler, a refrigerationcondensing unit or any other form of air cooled heat exchanger. Thewater is known in such systems to be discharged in the form of a finespray nebulized by passing the spray at high pressure through a smallorifice. Such water spray nozzle arrays are often also referred to as a“mister.”

Numerous problems exist in implementing such evaporative pre-coolerswith such heat exchangers or other air receiving equipment. Forinstance, large air cooled heat exchangers with multiple independentlystaged fans have highly complex and variable air flow. One section of adevice may have air flow of two feet per second while a differentsection of the same device may simultaneously have air flow of ten feetper second. Existing monoblock pre-cooler systems cannot adapt to thisair flow rate variability, and so either supply too much water or toolittle.

Supplying too much water wastes water and can damage a heat exchanger orturbine. In such cases liquid water is entrained into the air streamwhere it can do damage either through direct impingement or through thedeposition of dissolved solids on the heat exchanger.

Providing too little water flow results in lower efficiency gains thancould be achieved using the correct amount of water. Because such finemist water spray requires substantially constant high pressure foreffective operation, merely throttling water flow through a flow ratecontrol valve to provide variable water flow rates results indegradation of performance of the nebulizer and less fine spray, thusproviding an incomplete solution.

Some pre-cooler systems rely on rapid acting valves to control flow.This strategy presents a challenge to high pressure flash evaporativesystems. With a rapid acting strategy there are periods of both rampingup pressure and ramping down pressure. In both cases, pressure at thenozzle is at less than the optimal value for some period of time for aportion of the cycle. This portion of time in each cycle which is spentat sub-optimal pressure degrades high pressure nozzle performance.

Other types of pre-coolers which utilize saturated water pads and flowair through those pads are less than desirable for a variety of reasons.For instance, they have a tendency to shed large amounts of water intothe air flow which then can damage downstream equipment. Furthermore,large amounts of water require recycling, and such recycling systemswhich recirculate a bulk of the water therein have a tendency toconcentrate dissolved solids during recycling, ultimately leading toscale buildup and performance degradation. While chemical treatment(and/or periodic or continuous water discharge) can reduce scaleformation and biological growth, such chemical treatments (and/ordischarge) can present a negative ecological impact.

When sodden pads are utilized and droplet carry over is experienced, thedroplets of water, usually containing high levels of dissolved solids,impinge upon the conditioned device. This impingement can result inadditional scale buildup for downstream equipment and also potentiallydamage to downstream equipment through direct impingement.

Control systems for evaporative pre-coolers often utilize a temperaturesensor at the outlet of the heat exchanger and feed this temperaturesensor back to a controller which controls water flow into the system.These designs are problematic because the temperature response signalbecomes corrupted by heat rejected by the heat exchanger of the upgradedunit. For instance, when the heat exchanger is drawing a large amount ofheat from a working fluid within the heat exchanger, this outlettemperature will increase. However, the air entering the heat exchangermight already be saturated, and such a feedback signal willinappropriately add water flow beyond a point of saturation of the airwith associated negative consequences.

Other sensors for evaporative coolers may try to sense ambientpsychrometric conditions but fail to measure air flow to the device.Without knowing both airflow and psychrometric conditions, it is notpossible to calculate or deliver an appropriate mass of water for agiven air stream. Finally, due to the highly variable nature of airflowfor independently staged multi-fan systems, air streams must besegregated and analyzed independently to avoid delivering either toomuch or too little water.

SUMMARY OF THE INVENTION

With this invention, an evaporative pre-cooler is provided for useadjacent an air stream, such as an air stream feeding into a heatexchanger or turbine or other equipment which receives air therein. Thepre-cooler includes a plurality of water outlets. These water outletsinclude a nebulizer to discharge a fine spray of water into the airstream. To control the flow rate of water added to the air, the wateroutlets are divided into separate stages with each stage having at leasttwo water outlets and each water outlet associated with a singleseparate stage. A valve is provided for each stage to open and close thestage.

Each stage provides a known amount of water flow being discharged intothe air stream. Thus, when a certain amount of water flow into the airstream is desired, valves are opened associated with stages whose flowrates sum to the desired amount of water flow. Because the valves areeither open or closed, rather than throttling/pressure based flow rateadjustment valves, a high pressure is maintained and both well-nebulizedspray and precise water flow rates are delivered into the air stream.

To control the pre-cooler, typically a sensor package is provided whichsenses characteristics about the airflow to be cooled. This sensorpackage includes an anemometer or other air flow rate sensor and somemeasure of the humidity of the air within the air stream, such as wetbulb temperature and dry bulb temperature sensors. With such sensors andby characterizing the humidity of the air to be treated, and knowing anamount of humidity that can be added to the air, as well as knowing theflow rate of the air, an operator (or programmed/calibrated machine) cancalculate how much water flow rate to add to the air and then openassociated valves of associated stages to provide the moisture required.

When the airflow to be cooled is highly variable, such as at separateinlets of a multi-unit heat exchanger, such as a typical rooftop airconditioning heat exchanger of an industrial building, separate cellscan be provided which each measure separate airflow.

Humidity conditions can be shared amongst the individual cells orseparately measured also. Calculated amounts of moisture to add at eachcell can then be utilized to open and close valves associated withstages so that the precise proper amount of water is supplied in eachcell. As an alternative, if the separate heat exchanger units can becontrolled so as to have a common airflow rate thereinto, then a commonsignal can be provided to each cell with a common amount of moisturesupplied at each cell. Conceivably also, valves associated withindividual stages can supply water to multiple different cells in suchsystems where the heat exchangers are operating at a common airflowrate.

One form of equipment which effectively implements this system includescells which are in the form of housings with an open front and an openrear allowing the airflow to pass therethrough. Water outlets areprovided in the form of nozzles extending from bars located near theexit of this housing. The nozzles face forward, in a counter-flowdirection relative to the air stream, so that a mist pattern from eachnozzle tends to remain within the enclosure before the moistened air isdriven out of the exit. Housing depth is selected to so keep most of amist cloud from the nozzles within the housing.

A drift eliminator is preferably provided adjacent the exit whichprovides multiple separate curving cells through which the moistened airmust pass before leaving the housing. The drift eliminator keeps waterdroplets entrained within the airflow but not yet evaporated fromexiting the housing and doing damage downstream from the cell.

Each nozzle is associated with a separate stage. If the stage that anozzle is associated with is called for by the controller and theassociated valve for that stage is opened, high pressure water will flowto the nozzle and a fine spray will be discharged therefrom. Preferably,each bar has multiple lines therein with one line associated with eachstage. The nozzles are coupled to one of the lines associated with oneof the stages in a pattern which causes nozzles within a common stage tobe well separated from each other and in a generally evenly distributedpattern. Thus, when a single stage is on, a well distributed pattern offine spray is provided within the housing for even moistening of airpassing therethrough.

A lower portion of the housing preferably includes a drain therein whichcan draw away water, such as that resulting from direct contact of thefine spray with walls of the housing, and to some extent excess waterpulled from the drift eliminator. In addition, naturally occurringcondensate, such as from an evaporation coil can also be collected. Thiscondensed water will tend to be relatively low in dissolved solids.These water sources, together or separately, can be collected andperiodically pumped and recycled back to the water outlets. Suchperiodic recycling not only decreases water demand for the overallsystem but also acts as a form of purge in that the condensed water thatis recirculated tends to be exceptionally low in dissolved solids and socan tend to remove scale deposits which might otherwise collect withinthe system.

OBJECTS OF THE INVENTION

Accordingly, a primary object of the present invention is to provide anevaporative pre-cooler to decrease a temperature of air upstream of anair inlet of mechanical equipment.

Another object of the present invention is to provide an evaporativepre-cooler which increases a mass of air entering an air inlet ofmechanical equipment.

Another object of the present invention is to enhance efficiency of aheat exchanger by pre-cooling cooling air entering the heat exchanger.

Another object of the present invention is to enhance efficiency of apower plant by decreasing a temperature of combustion air entering thepower plant.

Another object of the present invention is to enhance efficiency of apower plant by increasing effectiveness of a heat exchanger and/ordecreasing a size of a heat exchanger required for the power plant byevaporatively pre-cooling air utilized for cooling of working fluidwithin the heat exchanger.

Another object of the present invention is to provide an evaporativepre-cooler which is adjustable to provide a proper amount of water toair for air saturation, and without excessive water usage.

Another object of the present invention is to provide an evaporativepre-cooler which recirculates condensing portions of water and run-offwater utilized thereby to minimize water consumption.

Another object of the present invention is to provide an evaporativepre-cooler which minimizes scale buildup within the pre-cooler systemitself and minimizes scale buildup for downstream equipment.

Another object of the present invention is to provide an evaporativepre-cooler which is modular in form to be deployable in a scalablefashion with smaller and larger mechanical equipment which receives airtherein.

Other further objects of the present invention will become apparent froma careful reading of the included drawing figures, the claims anddetailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a heat exchanger with a series ofpre-cooler cells associated with different heat exchanger units withinan overall heat exchanger system and showing how air flows through thepre-cooler cells before entering the heat exchangers.

FIG. 2 is a perspective view of a single cell with portions thereof cutaway and revealing interior details of the cell.

FIG. 3 is a side elevation full sectional view of the pre-cooler cell ofFIG. 2.

FIG. 4 is a schematic view of an alternative embodiment arrangement forseparate stages of water outlets according to an alternative embodimentof this invention.

FIG. 5 is a detail sectional view taken along line 5-5 of FIG. 3 andrevealing interior details within a bar supporting nozzles according toa preferred embodiment of this invention.

FIGS. 6-16 are schematic views of a preferred embodiment of thisinvention and showing how water flow rates from ten percent to onehundred percent of maximum can each be achieved by opening differentvalves for different stages of water outlets according to thisinvention.

FIG. 17 is a flow chart illustrating how water flows within the systemof this invention and particularly illustrating how partial waterrecirculation is achieved.

FIG. 18 is a table with one exemplary set of numbers for flow rates ofair and water within one typical evaporative pre-cooler system accordingto this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, wherein like reference numerals representlike parts throughout the various drawing figures, reference numeral 10is directed to a pre-cooler cell (FIGS. 1 and 2) for use alone ortogether adjacent a heat exchanger HX or system 1 of multiple heatexchangers HX to pre-cool air (arrow A of FIG. 1) entering the heatexchangers HX. The pre-cooler 10 evaporates water into the air to reducea temperature of the air and increase a mass of the air for enhancedeffectiveness of the heat exchanger HX. The cells 10 are configured tohave a precise and highly adjustable water flow rate while maintaining afine spray of water for consistent evaporative effectiveness, maximizingair temperature reduction while avoiding water droplet carryoverdownstream.

In essence, and with particular reference to FIG. 2, basic details ofthe pre-cooler cell 10 of this invention are described, according to amost preferred embodiment. The cell 10 includes a housing 20 as apreferred form of enclosure through which air passes (along arrow A) andreceives a fine spray of water (arrow B) to evaporatively cool the airinto humid air discharge flow (arrow C). Multiple valves 30 (FIG. 3)control water flow through a manifold 40 and to a plurality of nozzles60 which are supported on bars 50 within the housing 20. Each of thenozzles 60 is associated with one stage and each stage is associatedwith one of the valves 30. Multiple nozzles 60 are provided within eachstage and the valves 30 can be opened or closed so that a total numberof nozzles 60 desired can be opened so that a desired flow rate isachieved.

Most preferably, the nozzles 60 are oriented in a direction oppositethat of air flow A for maximization of residence time and mixing toachieve full evaporation of the fine mist of water discharged from thenozzles 60. A drift eliminator 70 is provided at an outlet side of thehousing 20. This drift eliminator 70 prevents less than fully evaporatedwater vapor from passing out of the housing 20, by providing a curvingpathway for the air to travel upon leaving the housing 20, and capturingsuch water vapor thereon.

An anemometer 80 is associated with the housing 20 to measure airflowthrough the cell 10. The anemometer 80 is configured to send a signal toa controller which opens and closes valves 30 according to anoperational program, and also potentially taking in other ambientconditions, such as wet bulb temperature and dry bulb temperature toprovide the flow rate of water into the cell 10 available for maximumevaporative cooling of the air A, or to achieve other design objectives.Additionally, a dry bulb temperature sensor 90 or other sensor relatedto humidity can be provided downstream of the cell 10 to monitor theeffectiveness of the cell 10 and provide feedback to the controller toincrease or decrease water flow through adjustment of the valves 30responsive to actual measurements provided at each cell 10.

An overall evaporative cooler system 100 can be configured with waterreclamation incorporated therein (FIG. 17). In such a system watercondensing within the cell 10 can be drained into a collection tank 110with an associated booster pump to pump the condensed water back to thecells 10 periodically, such that overall water demands are diminished.An ambient calculator 120 associated with the system 100 can measuresystem parameters such as wet bulb and dry bulb temperatures, orotherwise measure relative humidity or absolute humidity of the air, anduse this information along with anemometer 80 readings to feed into acontroller for effective control of the system 100.

More specifically, and with particular reference initially to FIG. 1,details of systems in which the evaporative pre-cooler of this inventioncan be used are described, according to a preferred embodiment. FIG. 1displays a multi-fan air cooled heat exchanger. Multiple cells 10 arearranged around the heat exchanger HX, such as with one cell 10 adjacenteach inlet for air adjacent each heat exchanger HX. Air entering theheat exchangers HX (along arrow A) must thus pass through the cells 10first. Such arrays of heat exchangers HX often have individually stagedfan arrangements so that the air speed of air passing through one cellmay be different than that passing through another cell.

In such systems, even though all surrounding air may have a similarhumidity, different cells 10 need to supply a different amount of waterfor evaporation within each cell 10 to accommodate these differing airflow rates. Even if all fans are operated at a single speed, andvelocity is common for all of the heat exchangers HX, there is still theopportunity to account for other ambient conditions, such as variabilityin temperature and/or humidity. For instance, adjacent equipment mightbe producing consistently higher temperatures on one side of the system1 than on the other side, so that cells 10 on one side are hotter thanon the other side.

Heat exchangers increase in effectiveness proportional to temperaturedifference between the heat transfer fluids. Hence, the cooler the airentering the heat exchanger HX, the more effective the heat exchanger.Furthermore, the greater the mass of the heat exchange fluid removingheat, the more effective the heat exchanger is, in that each unit massof heat transfer fluid can carry a greater amount of heat out of theheat exchanger HX. Thus, by cooling the air A and increasing a massdensity of the humidified air into humidified air (arrow C), a greateramount of heat transfer can occur through the heat exchanger HX. Eithersystem performance is enhanced in that the fluid being cooled is cooledto a lower temperature, or fans which draw cooling air A into the heatexchanger HX need not run as hard to provide sufficient air A forcooling. Ultimately, heat exchangers HX can be sized smaller if they areconfigured to operate more effectively.

Furthermore, many power plants operate on power production cycles whichhave an overall thermal efficiency which is proportional to changes intemperature of the working fluid. The cooler the working fluid is at aninlet of such power cycles, the greater thermal efficiency which can beobtained. For instance, with a combustion gas turbine operating on aBrayton cycle, the cooler the inlet air, the greater the thermalefficiency of the power plant, and hence the greater amount of powerthat can be generated for a given amount of fuel being combusted.

Depending on the equipment with which the cells 10 are to be utilized,the cells 10 can be scaled in size or can be provided in arrays ofgreater or lesser numbers of cells 10. When multiple cells 10 areutilized, they can be configured to operate independently and separatelywith their own controls and their own sensors. Alternatively, the cells10 can be to at least some extent integrated together such as byutilizing similar sensors, similar valves and similar water supply andwater recirculation systems.

With particular reference to FIGS. 2 and 3, details of each individualpre-cooler cell 10 are described, according to a most preferredembodiment. Each pre-cooler cell 10 preferably has a similarconfiguration to other cells 10. Each cell 10 includes an outer housing20 which is a substantially complete enclosure except for an inlet 26and outlet 28 for air A to enter into the cell 10 and exit as humid airout (arrow C of FIGS. 2 and 3). The housing 10 includes a floor 21opposite a cap 22. Sides 25 extend up from the floor 21 to the cap 22.Preferably, the sides 25 are parallel with each other and the floor 21and cap 22 are parallel with each other and perpendicular to the sides25, so that the housing 20 is generally rectangular/square incross-section.

A lattice 24 is preferably provided which spans the inlet 26. Thislattice 24 can tend to keep debris out of the housing 20 or can be usedto mount a pre-filter to enhance the same effect, as well as keepingwater spray contained. A depth of the housing 20 between the inlet 26and outlet 28 is sized so that the water spray within the housing 20from the nozzles 60 tends to remain substantially within the housing 20.Thus, the housing 20 defines a reaction chamber where the water isevaporated fully into the air A, before exiting the housing 20 ashumidified cooled air C.

The floor 21 not only defines a wall of the housing 20 but alsopreferably acts as a drain pan with a drain included at a low point ofthe floor 21. Thus, any non-evaporated water occurring within thehousing 20 is captured for potential recycling, as described in detailbelow.

A plurality of valves 30 are preferably associated with each cell 10,and typically mounted on the cap 22 under an optional cover 23 toprotect the valves 30 from weathering, solar radiation or damage fromother surrounding environmental conditions. An array of such valves 30is preferably configured so that one valve 30 is provided for each stagewithin each cell 10. In a preferred cell 10 four stages are provided sothat four valves 30 are provided. Each valve 30 is coupled to a highpressure water main line 32. This main line 32 preferably supplies eachof the cells 10 with high pressure water from a single high pressurepump package 106 (FIG. 17) or other high pressure water source. Highpressure water is utilized to ensure that the nozzles 60 maintainoptimal performance and nebulize the water being discharged by thenozzles 60.

Each valve 30 includes a body 34 and a control 36 which interacts with avalve element within the body 34. An outlet 38 is provided opposite thehigh pressure water main line 32. This outlet 38 feeds a manifold 40which splits up the water for each stage associated with the valve 30and sends it to multiple separate lines located within multiple separatebars 50 (FIG. 5) for ultimate routing to nozzles 60 associated with thestage to which the valve 30 is coupled.

The valves 30 are preferably of a type which transitions between eithera fully open or a fully closed position, as opposed to being a variableflow rate valve. Thus, when the valves 30 are open the pressure dropacross the valve 30 is negligible. When the valve 30 is closed, no flowacross the valve 30 occurs. The control 36 interacts with the valveelement within the body 34 to cause the valve 30 to transition betweenan open and a closed state depending on signals received from a centralcontroller associated with each cell 10, or conceivably a controllerwhich serves all of multiple cells 10.

Each valve 30 is associated with a single stage, as well as a separatemanifold 40 (FIGS. 3 and 4). The manifold 40 has separate lines 42.These lines typically include junctions 44 (FIG. 4) which allow themanifold 40 to direct water to separate lines 42 which are in parallelwith each other. These lines 42 can then pass into individual bars 50.Most preferably, each bar 50 has multiple lines 42 therein, with atleast one line 42 associated with each stage (FIG. 5). As analternative, and as shown in FIG. 4, conceivably only one line 42, ormultiple lines 42 but less than the number of stages, could be suppliedto each bar 50. In the system depicted in FIG. 4, the separation of thestages and the individual valves 30 associated with each stage can bemost readily seen. However, the nozzles 60 tend to be somewhat tightlygrouped together for less than optimal distribution to all of the airentering the housing 20, in the embodiment of FIG. 4. Thus, preferablyeach bar 50 has nozzles 60 associated with different stages on each bar50 to better distribute nozzles 60 within a common stage away from eachother.

The nozzles 60 preferably face in a direct counter flow direction (alongarrow B of FIGS. 2 and 3). Alternatively, the nozzles 60 could be angledsomewhat in different directions to better enhance their ability todirect fine spray of water uniformly within the housing 20. While theembodiment of FIG. 4 shows a single line fed to each bar 50 and witheach nozzle 60 of each bar 50 being associated with the stage that thatbar 50 is coupled to, most preferably, each bar 50 has multiple linespassing thereinto with the lines coming from different stages and withthe nozzles 60 on the bar 50 coupled through tees 43 to different stageswithin a single bar.

For instance, and with reference to FIG. 5, line 42A is shown associatedwith stage one and line 42B is shown associated with stage two, withline 42C and line 42D associated with stages three and four,respectively. A tee 43A is formed in line 42A which feeds one of thenozzles 60. A next adjacent nozzle 60 within the same tube 50 has a tee43B associated with line 42B coupled thereto.

FIGS. 6-16 show various different states for the overall array ofnozzles 60. In FIG. 6 a state is shown where all of the stages areclosed and hence all of the nozzles 60 are off. In FIG. 7, a ten percentflow arrangement is illustrated where only stage one is open and so thefive nozzles 60 associated with stage one are open. In FIG. 8 a state isillustrated for twenty percent flow where only the nozzles 60 associatedwith stage two are open. Note that twice as many nozzles 60 areassociated with stage two as with stage one (ten nozzles 60 rather thanfive nozzles 60). In FIG. 9 a state is illustrated where only thenozzles 60 associated with stage three are open, so that thirty percentof maximum flow is provided. In FIG. 10 a state is illustrated whereonly nozzles 60 associated with stage four are open, so that fortypercent of maximum water flow is provided.

While the stages herein are shown as having different amounts of waterflow accommodated by having different numbers of nozzles 60, a similareffect can be provided by having a common number of nozzles 60 with eachstage but having the nozzles 60 sized larger for some of the stages.Alternatively, each of the stages could have a common number of nozzles60 so that increasing flow rate would involve opening multiple stages.

Most preferably, and as depicted in FIGS. 6-10, stages one, two, threeand four include different numbers of nozzles 60 of similar sizes sothat they provide respectively ten, twenty, thirty and forty percent ofmaximum flow. To provide fifty percent of maximum flow, multiple stagescan be open at the same time, such as stage one and stage four or stagetwo and stage three. To achieve sixty percent flow, stage four and stagetwo can be open together or stage one, stage two and stage three caneach be open together. To achieve seventy percent of flow, stage fourand stage three can be open or stage four, stage two and stage one canbe open together. To achieve eighty percent of flow, stage four would beopen along with stage three and stage one. To achieve ninety percent offlow, stage four would be open along with stage three and stage two. Tohave maximum flow provided, each of stages one, two, three and fourwould be simultaneously open. Additionally, pump pressure variationabove a minimum necessary, can be used to provide further adjustment ofwater flow rate through use of a variable speed, variable pressure pump.In this way flow rates between the percentages listed above could beprovided.

These various states and the amount of flow provided are sequentiallyillustrated in FIGS. 6-16. Each circle represents a separate nozzle 60and the nozzles 60 are arrayed upon bars 50 with separate lines 42located within each bar 50, as shown in the detail of FIG. 5. In thispreferred embodiment, each bar 50 has an inlet 52 (FIGS. 2 and 3) at oneend through which each of the lines 42 can enter the bar 50. An end 54opposite the inlet 52 allows for attachment of the bar 50 within thehousing 20, preferably adjacent the outlet and oriented with a long axisthereof extending substantially vertically. A face 56 of each bar 50includes the nozzles 60 extending therefrom and faces toward the inlet26 of the housing 20.

Each nozzle 60 preferably has a small orifice 64 within a cap 62 on aside of each nozzle 60 facing toward the inlet 26 of the housing 20. Thesize of the orifice 64 is carefully selected and shaped to maximizeatomization of water spray passing therethrough. Pressure within eachstage is maintained sufficiently high, and orifice 64 size issufficiently small so that the nozzles 60 maintain their optimalperformance providing a fine nebulized spray from each nozzle 60.

Because the flow rate is not controlled by a variable flow rate valve,which inherently also effects pressure, but rather by having separatestages which can be selectively added together or subtracted therefromto provide the desired flow rate, flow rate adjustment is providedindependent of pressure. Thus, the high pressure required for optimalperformance of the nozzles 60 is not degraded as the flow rates aredecreased by throttling a valve. Rather, even flow rates as low as tenpercent of maximum can be achieved with the stage one valve 30 wide openand all of the other valves 30 closed. No pressure-controlling valve isin a partially open and pressure reducing state, but rather the nozzles60 receive full pressure at all times. Thus, the nozzles 60 which arereceiving water flow provide a fine nebulized mist of water (arrow B ofFIG. 2) which forms a cloud within the housing 20. The airflow Aentering the housing 20 readily evaporates this fine mist of water, inturn reducing the temperature of the air and increasing the humidity ofthe air before exiting the housing 20 along arrow C.

Preferably, the housing 20 includes a drift eliminator 70 adjacent theoutlet 28. Due to the relatively laminar flow nature of the air enteringeach individual cell, some of the droplets can become entrapped in aband of saturated air and not be able to complete the evaporationprocess. For this reason, an absorptive media drift eliminator 70 isprovided in the air stream downstream from the nozzles 60. The drifteliminator 70 causes the air to make rapid turns before entering theconditioned device, such as the heat exchanger HX (FIG. 1). Due to theirgreater mass, the water droplets are not able to make those turns asrapidly, thus resulting in impact with the drift eliminator 70. Thedrift eliminator 70 is preferably formed of a material which is somewhatabsorbent and is readily thus wetted. This wetted surface can give upadditional moisture to drier portions of the airflow A. If the wettedportions are over-saturated, gravity pulls the excess water down throughthe drift eliminator 70 down to the floor 21 of the housing 20 forexcess water collection, as described in detail below.

The drift eliminator 70 thus acts differently from a fully irrigatedmedia pre-cooler pad constructed of similar material. First, as a drifteliminator 70, the amount of water that impacts the drift eliminator 70causes it to become damp, whereas a pad in a traditional fully irrigatedpre-cooler is typically completely sodden, with rivulets of liquid waterflowing down both faces. This is important because typically completelysodden pads are much more likely to have droplet carryover. When dropletcarryover occurs, these droplets of water usually containing levels ofdissolved solids, impinge upon the conditioned device. In most casesthis will result in significant scale buildup and has been the principlebarrier to market penetration of pre-coolers utilizing fully irrigatedevaporation pad technology.

Secondly, since the drift eliminator 70 is only being used for driftelimination, the absorptive material used can be significantly thinner.Typical absorptive media pads for fully irrigated pre-cooler systems arefrom six inches to twelve inches in thickness, whereas the drifteliminator 70 of this invention can be from one to six inches in depth.The combination of reduced thickness and reduced water loadingsubstantially reduces both the operational weight and airflow resistanceof the described device when compared to fully irrigated pre-coolers.

Finally, the surface area of the droplets is larger by an order ofmagnitude or more than the surface area of the largest fully irrigatedevaporative pre-coolers. Greater surface area results in superiorcooling performance at a lower weight while the reduced water load onthe material largely eliminates carryover based equipment degradationeffects. Edges 74 of the drift eliminator 70 reside against the sides25, floor 21 and cap 22, so that the airflow A passes through the cells72 within the drift eliminator 70. If the air A has water dropletsentrained therein they will be deposited upon the surfaces of the drifteliminator 70. If the air A is not yet fully saturated, the wet surfacesof the drift eliminator 70 provide a source of water for furtherevaporation towards saturation of the air A.

With particular reference to FIGS. 17 and 18, the operation of the cells10 within an overall system 100 for pre-cooling with water reclamationare described. The system 100 includes a series of pre-coolers 10 fed bythe high pressure water line 32. This water line 32 is in turn fed froma pump package 106 if necessary to raise the pressure to the requiredlevel. Most preferably, at least two separate feed valves 104 or asingle valve which can switch from different sources is providedupstream of the pump package 106 or otherwise upstream of the highpressure main line 32. The main line 32 can thus be fed either from aprimary source of water, such as a municipal water supply 102, or from asecondary source of water such as a collection tank and associatedbooster pump 110 which receives recycled water from drains of thepre-coolers 10, along a drain line 108.

An ambient calculator 120 receives as input information related tohumidity of the surrounding air, such as wet bulb and dry bulbtemperatures. Air flow rates can also be part of the ambient calculator120, such as through use of the anemometer 90. This anemometer is shownas a fan blade impeller that rotates about an axis aligned with thedirection of flow. Alternatively, the anemometer could have an impellermounted to an axis transverse to the air flow. As another alternative,an air flow rate signal can be provided from a fan associated with theheat exchanger HX (FIG. 1) or other equipment adjacent the cell 10. Thesignal could be a variable fan speed control signal or a mastercontroller signal that correlates to the speed desired for the fan, orcould be a tachometer coupled to the fan itself. With these sensorreadings, desired flow rates can be calculated and in turn specificcontrols for the valves 30 (FIGS. 1, 3 and 4) can be chosen foroperation of the system 100.

In particular, the calculator or other controller can receive the drybulb temperature, ambient relative humidity, wet bulb temperature,either calculated or measured, to calculate absolute humidity in grainsper pound of dry air. This absolute humidity is defined as one hundredpercent relative humidity at ambient wet bulb temperature in grains perpound of dry air. The absolute humidity in grains per pound of dry aircan then be subtracted from the relative humidity in grains per pound ofdry air to determine how much water in terms of grains per pound of dryair can be added to the air.

This amount is then divided by the maximum mass of water that can bedelivered to a pound of dry air, measured in grains. Ten percent of thisamount (rounded down), equals a flow rate for stage one. Twenty percentof this amount (rounded down), equals a flow rate for stage two. Thirdand fourth stages can in turn be twenty and thirty percent of thisamount (rounded down). This criteria can then be used for sizing of thenozzles 60 when initially configuring the system. Thereafter, uponsensing airflow in ambient conditions, the local controller can set theproper mass of water flow actuating one or more of the several valves 30either individually or in concert to achieve the percentage desired ofmaximum airflow.

While this preferred algorithm can be executed by this invention, otheralgorithms could similarly be utilized. For instance, taking intoaccount known typical environmental conditions and the typicalavailability of air to receive additional humidity, before saturation, atypical maximum rate can be identified. This maximum amount can then bedivided into subparts to be provided by each of the stages in theinitial design.

In an embodiment typical for this invention, four stages are provided,but different numbers of stages could be provided in the alternative. Inone embodiment, stage one is provided which is controlled by a valvewhich feeds eight separate nozzles 60 which total 0.1 gallons per minutein flow rate. Stage two includes sixteen nozzles 60 totaling 0.2 gallonsper minute. Stage three has twenty-four nozzles 60 totaling 0.3 gallonsper minute and stage four has thirty-two nozzles 60 totaling 0.4 gallonsper minute. Different combinations of the stages yield to different massof water as is needed to saturate the air down to wet bulb temperature.For example, if the controls calculate that 0.7 gallons per minute areneeded to achieve saturation, then stages three and four can be operatedin conjunction. In this way, a variable mass of water can be admitted tothe air stream (0.1 gallons per minute, 0.2 gallons per minute, etc.)without dropping below the minimum operating pressure at the nozzle 60.

Maintaining minimum operating pressure at the nozzle 60 is critical forflash evaporative cooling operation. Evaporative performance is linkedto droplet size, and droplet size is in turn linked to pressure at thenozzle. However, a need for variable mass water flow conflicts with thisneed for constant pressure at the nozzle. A staged nozzle 60 system asdescribed herein avoids the problems inherent with current controlmethodologies as the pressure remains constant and flexibility of flowrate is still provided. The addition of a variable speed/pressure pumpallows a virtually limitless number of flow rates, all in pursuit ofproviding a proper mass of water to saturate the air without producingcarryover. For instance, in addition to the stages, some small amount ofpressure regulation and/or speed of an associated pump can be controlledto fine tune the system while still maintaining minimum pressurerequired for nozzle 60 performance. Such a staged system is thus able toprovide variable and precise flow control without the problemsassociated with previous examples of pressure variation.

While the vast majority of water emitted from the nozzle 60 within thepre-coolers 10 immediately convert to vapor, nozzle type cells 10 alsomay have a small amount of unevaporated water that collects on surfacesof the housing 20 due to impact with walls of the housing 20 itself. Inthe preferred embodiment of the system 100, such non-evaporated excesswater is conducted away by way of collection drains along drain line 108and routed to a collection tank 110. Condensate drains from evaporatorcoils can also be routed to a common collection tank or to a separatecondensate only collection tank.

When the collection tank 110 is full, controllers shut the valve comingfrom a primary water source, such as the municipal water supply 102 andopen valves from the collection tank system 110. When the high pressurepumps are next engaged, an optional booster pump associated with thecollection tank 110 goes into operation to supply inlet water to thehigh pressure pump package 106. When the collection tank empties,controls close the valve from the outlet of the booster pump associatedwith the collection tank 110 and turn off the booster pump. The valvefrom the primary water source is simultaneously opened.

Use of a collection tank 110 in conjunction with the flash evaporativesystem delivers many benefits. First, condensate from evaporator coils(alone or mixed with the non-evaporated excess water from the drain line108) can be utilized as feed water for the pre-coolers 10. Use ofcondensate in this matter not only reduces overall water consumption bythe system, but also reduces the volume of water which is discharged towaste water treatment plants. Additionally, because of the extremely lowlevels of dissolved solids in condensate drain water, a periodicflushing of the pump and pre-cooler condensate acts as a solventremoving any potential buildup of dissolved solids before they can formperformance degrading scale. While a small amount of water will bereturned to the cells 10 for reutilization, the binary nature of waterthat is admitted to the pump system either the primary water source suchas the municipal water supply 102, or water from the collector tank 110in the form of excess non-evaporated water and/or condensate water,means that the system as a whole remains essentially single pass innature. A single pass system has several benefits. First, a single passsystem will not increase the concentration of dissolved solids in therecirculating water in the way that a recirculator system would. Thisreduces the opportunity for scale formation that has proven to be such achallenge for previous evaporative pre-cooler technologies.Additionally, a single pass system does not need to periodicallydischarge saturated water solutions into the waste water treatmentsystem.

An alternative embodiment of the cells 10 disclosed herein is to utilizeultrasonic nebulizers in place of the nozzles 60 for the injection ofwater vapor into the air stream A. Multiple nebulizers can be used in acell 10, with the same type of proportional flow control as in thepreferred embodiment through multiple separate stages. Thus, the preciseamount of water is provided as directed by the controller and asindicated by ambient conditions to provide saturated water withoutexcess condensing water flow leaving the cells 10.

This disclosure is provided to reveal a preferred embodiment of theinvention and a best mode for practicing the invention. Having thusdescribed the invention in this way, it should be apparent that variousdifferent modifications can be made to the preferred embodiment withoutdeparting from the scope and spirit of this invention disclosure. Whenstructures are identified as a means to perform a function, theidentification is intended to include all structures which can performthe function specified. When structures of this invention are identifiedas being coupled together, such language should be interpreted broadlyto include the structures being coupled directly together or coupledtogether through intervening structures. Such coupling could bepermanent or temporary and either in a rigid fashion or in a fashionwhich allows pivoting, sliding or other relative motion while stillproviding some form of attachment, unless specifically restricted.

1. An evaporative pre-cooler with variable water flow, comprising incombination: a support interposed within an air stream to be cooled; aplurality of water outlets coupled to said support and oriented todischarge water into the air stream; said plurality of water outletseach including a nebulizer, such that the water is discharged as a finespray; a source of water coupled to said plurality of water outlets andupstream of said plurality of water outlets; each of said plurality ofwater outlets coupled to one of at least two valves downstream of saidsource of water, with each said water outlet that is coupled to a commonvalve discharging water from said source of water when said common valveis open; and a controller adapted to operate said at least two valves tocause a water flow rate into the air stream to be varied.
 2. Theevaporative pre-cooler of claim 1 wherein said nebulizer includes anultrasonic nebulizer.
 3. The evaporative pre-cooler of claim 1 whereinsaid nebulizer includes a sufficiently small hole in each of saidplurality of water outlets, in conjunction with a sufficiently highpressure of water upstream of said plurality of water outlets that waterexiting said hole is atomized into a fine spray.
 4. The evaporativepre-cooler of claim 3 wherein said valves and lines coupling said sourceof water to said water outlets through said valves are each sized tofacilitate a greater flow rate of water than a sum of water outlet flowrates for water outlets associated with each said valve, such thatpressure upstream of said water outlets is maintained.
 5. Theevaporative pre-cooler of claim 4 wherein a pump is interposed betweensaid source of water and said at least two valves, said pumppressurizing water upstream of said valves to a pressure greater than aminimum pressure required to maintain nebulizer fine spray performanceat said water outlets.
 6. The evaporative pre-cooler of claim 1 whereinsaid water outlets coupled to said common valve of said at least twovalves define a stage, with a number of said stages equal to a number ofsaid valves downstream of said source of water, each of said stageshaving at least two water outlets therein, and wherein said wateroutlets of each said stage are spaced apart to decrease concentration ofwater within the air stream when said valve associated with said stageis open and each of said water outlets associated with said valve isdischarging water.
 7. The evaporative pre-cooler of claim 6 wherein aplurality of bars are oriented extending transverse to the air stream,said bars supporting a plurality of said water outlets thereon, saidwater outlets of each said bar coupled to at least two separate stages.8. The evaporative pre-cooler of claim 1 wherein said support includes apartial enclosure surrounding the air stream on lateral sides of the airstream, and with an open front and rear, with the air stream enteringsaid front of said enclosure and exiting said rear of said enclosure,said enclosure having a depth between said front and said rear at leastas great as a majority of spray distance of said fine spray of waterdischarged from said plurality of water outlets.
 9. The evaporativepre-cooler of claim 8 wherein said water outlets are located closer tosaid rear than to said front and with said water outlets facing at leastpartially toward said front of said enclosure.
 10. The evaporativepre-cooler of claim 8 wherein a drift eliminator is located adjacentsaid rear of said enclosure, said drift eliminator having a plurality ofopen cells passing entirely therethrough and adapted to allow the airstream to pass through said cells in said drift eliminator, said cellshaving an at least somewhat curving path such that the air stream isrequired to curve while passing through said cells of said drifteliminator.
 11. The evaporative pre-cooler of claim 10 wherein saidwater outlets are located adjacent said drift eliminator and facing awayfrom said drift eliminator.
 12. The evaporative pre-cooler of claim 11wherein a drain is located below said drift eliminator, said drainadapted to collect water condensing on said drift eliminator and fallingdown off of said drift eliminator, said drain coupled to said pluralityof water outlets through a pump upstream of said water outlets, suchthat water condensing on said drift eliminator is at least partiallyrecycled back to said water outlets.
 13. The evaporative pre-cooler ofclaim 1 wherein an anemometer is coupled to said support and oriented tomeasure a flow rate of the air stream to be cooled, said anemometercoupled to said controller to supply a signal related to speed of theair stream to be cooled.
 14. The evaporative pre-cooler of claim 13wherein a humidity sensor is coupled to said support and positioned tomeasure humidity of the air stream to be cooled, said humidity sensoradapted to send a signal to said controller indicative of humidity ofthe air stream to be cooled.
 15. The evaporative pre-cooler of claim 1wherein a sensor is located downstream of said water outlets, saidsensor adapted to measure humidity of the air stream after the airstream has been cooled by evaporation of the fine spray of waterdischarged by said plurality of said water outlets, said sensorsupplying a signal in the form of feedback to the controller to adjust awater flow rate from said plurality of water outlets responsive tohumidity sensed by said humidity sensor downstream from said wateroutlets.
 16. The evaporative cooler of claim 1 wherein said support islocated adjacent an air inlet of an air receiving mechanical device witha fan therein, said fan generating the airflow, a signal associated withspeed of said fan coupled to said controller to supply a signal relatedto speed of the air stream to be cooled.
 17. A water evaporationpre-cooler, comprising in combination: a plurality of water outletsoriented to discharge water into an air stream; said plurality of wateroutlets each including a nebulizer, such that the water is discharged asa fine spray; a primary source of water coupled to said plurality ofwater outlets upstream of said plurality of water outlets; a drain belowsaid plurality of water outlets, said drain adapted to collect condensedwater from said water outlets; said drain routed to a secondary sourceof water coupled to said plurality of water outlets upstream of saidplurality of water outlets; and at least one feed valve upstream of saidplurality of water outlets, said at least one feed valve adapted tocontrol which of said primary source of water and said secondary sourceof water supplies water to said plurality of water outlets.
 18. Thewater evaporation pre-cooler of claim 17 wherein said primary source ofwater has a greater water capacity than said secondary source of water.19. The water evaporation pre-cooler of claim 18 wherein said primarysource of water has a water capacity greater than twice a capacity ofwater in said secondary source of water.
 20. The water evaporationpre-cooler of claim 19 wherein said primary source of water has a watercapacity at least ten times greater than a water capacity of saidsecondary source of water.
 21. The water evaporation pre-cooler of claim17 wherein said secondary source of water has a lesser amount ofdissolved solids contained therein than said primary source of water.22. The water evaporation pre-cooler of claim 17 wherein a drifteliminator is located downstream of said water outlets, said drifteliminator having a plurality of open cells passing entirelytherethrough and adapted to allow the air stream to pass through saidcells in said drift eliminator, said cells having an at least somewhatcurving path such that the air stream is required to curve while passingthrough said cells of said drift eliminator.
 23. The water evaporationpre-cooler of claim 22 wherein an enclosure surrounds at least portionsof the air stream to be cooled, said enclosure including an entranceopposite an exit with said entrance adapted to receive said air streamtherein and said exit adapted to discharge said air stream therefrom,said enclosure including a floor on one lateral side of the air streamextending between said entrance and said exit, said floor having saiddrain therein, said floor located beneath said drift eliminator, saiddrift eliminator located adjacent said exit of said enclosure.
 24. Thewater evaporation pre-cooler of claim 23 wherein said water outlets arelocated adjacent said drift eliminator and oriented to spray said finespray of water at least partially toward said entrance of saidenclosure.
 25. The water evaporation pre-cooler of claim 24 wherein eachof said plurality of water outlets is coupled to one of at least twovalves downstream of both said primary source of water and saidsecondary source of water, with each said water outlet that is coupledto a common valve discharging water when said common valve is open. 26.The water evaporation pre-cooler of claim 25 wherein said water outletscoupled to said common valve of said at least two valves define a stage,with a number of said stages equal to a number of said valves downstreamof said source of water, each of said stages having at least two wateroutlets therein, and wherein said water outlets of each said stage arespaced apart to decrease concentration of water within the air streamwhen said valve associated with said stage is open and each of saidwater outlets associated with said valve is discharging water.
 27. Thewater evaporation pre-cooler of claim 26 wherein a plurality of bars areoriented extending transverse to the air stream, said bars supporting aplurality of said water outlets thereon, said water outlets of each saidbar coupled to at least two separate stages.
 28. A method for cooling anair stream, including the steps of: providing a plurality of wateroutlets oriented to discharge water into the air stream, the pluralityof water outlets each including a nebulizer, such that the water isdischarged as a fine spray, a source of water coupled to the pluralityof water outlets and upstream of the plurality of water outlets, each ofthe plurality of water outlets coupled to one of at least two valvesdownstream of the source of water, with each water outlet that iscoupled to a common valve discharging water from the source of waterwhen the common valve is open, and a flow rate controller coupled to thewater outlets and adapted to control a rate of flow out of the wateroutlets; determining an amount of water flow needed to cool the airstream a desired amount by evaporation of the water into the air stream;and adjusting the at least two valves to adjust a number of wateroutlets discharging water to more closely match the needed amount ofwater flow.
 29. The method of claim 28 including the further step ofdefining water outlets coupled to a common valve as being associatedwith a common stage, with a number of stages equaling a number ofvalves, with each stage having a corresponding water flow rate whenopen; and selecting stages to be open as needed to total the desiredamount of water flow.
 30. The method of claim 29 including the furtherstep of spacing water outlets within common stages so that when a stageis operating water outlets associated with the operating stage arespaced apart to distribute water evenly within the air stream.
 31. Themethod of claim 30 including the further step of dividing the air streaminto separate portions and providing separate cells associated with eachportion of the air stream to be cooled, the separate cells eachincluding a separate enclosure which surrounds at least portions of theair stream to be cooled, said enclosure including an entrance oppositean exit with the entrance adapted to receive the air stream therein andthe exit adapted to discharge the air stream therefrom, the enclosureincluding a floor on one lateral side of the air stream extendingbetween the entrance and the exit.
 32. The method of claim 31 includingthe further step of collecting unevaporated water from the air stream byproviding a drift eliminator adjacent each exit, the drift eliminatorhaving a plurality of open cells passing entirely therethrough andadapted to allow the air stream to pass through the cells in the drifteliminator, the cells having an at least somewhat curving path such thatthe air stream is required to curve while passing through the cells ofthe drift eliminator.
 33. The method of claim 31 wherein said dividingstep includes the step of configuring each cell to have the floorthereof located beneath the drift eliminator and adjacent the exit ofthe enclosure.
 34. The method of claim 33 including the further step ofconfiguring each cell to have a separate controller and separate valvesfor independent operation of the separate cells on an associated portionof the air stream.
 35. The method of claim 33 wherein the separate cellsinclude a common controller and common valves with each stage having atleast one water outlet associated with each cell.
 36. The method ofclaim 28 including the further step of locating a drain below saidplurality of water outlets, the drain adapted to collect condensed waterfrom the water outlets, the drain routed to a secondary source of watercoupled to the plurality of water outlets upstream of the plurality ofwater outlets, and locating at least one feed valve upstream of theplurality of water outlets, the at least one feed valve adapted tocontrol which of the source of water and the secondary source of watersupplies water to the plurality of water outlets.
 37. The method ofclaim 36 wherein the secondary source of water has a capacity less thana capacity of the source of water.
 38. The method of claim 37 includingthe further step of cycling the feed valve to cause the water outlets toperiodically receive water from the secondary source of water, thesecondary source of water having a lesser amount of dissolved solidstherein, such that said cycling step purges dissolved solids from waterlines upstream of the plurality of water outlets.